Several members of the royal family and important Saudi businessmen were suddenly and unexpectedly arrested in a broad roundup over the weekend. And the president of the United States is dashing off late-night tweets, trying to get the Kingdom to bestow a tremendous, highly anticipated stock offering to Wall Street.

Here's the background:

Prince Alwaleed Bin Talal

Prince Alwaleed Bin Talal is one of the most internationally famous members of the Saudi royal family — but that doesn't necessarily make him popular at home. In fact, reports indicate he was arrested over the weekend along with other top Saudis in a supposed anti-corruption crackdown.

Saudi Prince Alwaleed bin Talal.

Mary Catherine Wellons | CNBC

Bin Talal is a billionaire investor who runs Kingdom Holdings and owns large stakes in companies like Twitter and News Corp. He comments regularly on Western television, speaking to CNBC just in October about the future of bitcoin and electric vehicles.

The billionaire is U.S.-educated and a philanthropist: In 2015, Bin Talal announced he would donate his entire fortune to help build a "better world of tolerance, acceptance, equality and opportunity for all."

Crown Prince Mohammed Bin Salman

Although Saudi officialdom is characterizing the weekend's arrests as part of a fight against corruption, many see the surprise detentions as a power play by Crown Prince Mohammed Bin Salman.

The prince, 32, has made a meteoric rise from relative obscurity to his father King Salman's direct heir and top advisor. He is overseeing the anti-corruption push, which was announced just a few hours before the first arrests were made.

Bin Salman leads the Kingdom's "Vision 2030" and the related "National Transformation Plan" — a program aimed at diversifying the Saudi economy beyond oil production. He is believed to have played a key role in Riyadh's decision to isolate Qatar.

"This is the latest act of concentration of power in Saudi," said Hasnain Malik, global head of equity research at investment bank Exotix Capital, adding that "as unprecedented and controversial as it may be, this centralisation might also be a necessary condition for pushing the austerity and transformation agenda" Bin Salman is overseeing.

In June, Saudi Arabia removed then-crown prince Muhammad Bin Nayef from his role and replaced him with Bin Salman.

That move immediately made the target on Bin Salman's back even bigger, and could have precipitated an intra-family power struggle.

Prior roles for Bin Salman include both defense minister and deputy crown prince, and he was earlier this year credited with a "huge success" after President Donald Trump made a decision to visit Saudi Arabia.

How do they connect to Trump?

Trump has ties to both the Crown Prince Bin Salman and the billionaire investor Bin Talal.

In addition to having likely orchestrated Trump's trip to Saudi Arabia, Bin Salman has reportedly developed a relationship with White House advisor Jared Kushner — the husband of the president's daughter and another 30-something man who has ridden family connections to the center of the world stage.

President Donald Trump meets with Mohammed bin Salman of Saudi Arabia, in the Oval Office at the White House, March 14, 2017 in Washington, DC.

Getty Images

As for Bin Talal, he and the president go back at least to the 1990s.

Between 1991 and 1995, Bin Talal came to the rescue of Trump, whose real estate empire was in financial trouble. Bin Talal purchased a yacht from the New York real estate mogul and was part of a group that helped take the city's floundering Plaza Hotel off Trump's hands.

But things have not been amicable between the two billionaires of late.

In 2015, Bin Talal bashed Trump for his rhetoric during the presidential campaign, and even called for him to drop out.

"You are a disgrace not only to the GOP but to all America," he said in a Twitter post. "Withdraw from the U.S presidential race as you will never win."

Trump responded: "Dopey Prince @Alwaleed_Talal wants to control our U.S. politicians with daddy's money. Can't do it when I get elected. #Trump2016"

How does this connect to Saudi Aramco?

The United States has many reasons to be interested in Saudi Arabia, including its oil and the central role it plays in Middle East politics, but the president has in the last two days zeroed in on something more specific: a win for Wall Street.

Trump called for the Kingdom to have Saudi Aramco, its state oil company, list shares on a U.S. stock exchange. That IPO is expected to be the biggest in history, and it has had exchanges around the world scrambling to land it.

Trump said over the weekend in a Twitter post that he hopes the IPO will go to the New York Stock Exchange. He then followed up, telling reporters aboard Air Force One that the Saudi king had told him "they will consider using U.S. exchanges."

—CNBC's Nyshka Chandran and Javier David and Reuters contributed to this report.